Situations or events occur where high-value data files are generated by numerous users for submittal to the event authority, and where it is imperative to assure the files are original as created during the authorized time period and location of the event. In various embodiments, such a situation or event may be for example, without limitation, a test or exam, such as a computer-based academic or professional exam (e.g., state bar exam, final exam for a college course, etc.), or the like, wherein the examinee provides answers or inputs which create or populate a data file in one or more memory devices of a computer (e.g., a PC, such as a laptop PC). Submittal of data files may occur at any time following the creation of the files, thus a highly secure method for prevention or detection of substitution of the files is needed.